Jim Ledwell Awarded Agassiz Medal by National Academy of Sciences

Senior Scientist Specializes in the Use of Chemical Tracers to Observe Currents in the Ocean

Oceanographer Jim Ledwell of the Woods Hole Oceanographic
Institution (WHOI) has been selected as the winner of the 2007 Alexander
Agassiz Medal, awarded by the U.S. National Academy of Sciences (NAS). Ledwell,
a senior scientist in the Department of Applied Ocean Physics and Engineering,
specializes in the use of chemical tracers to observe currents in the ocean.

Established in 1913, the Agassiz Medal is awarded every
three years to an individual scientist for original and fundamental contributions
to oceanography. The medal and prize of $15,000 will be officially presented to
Ledwell at an April 29 ceremony in Washington,
DC.

Ledwell was specifically cited by the Academy for his
"innovative and insightful tracer experiments using sulfur hexafluoride to
understand vertical diffusivity and turbulent mixing in the open ocean."
To measure the mixing and stirring effects of eddies and internal waves,
Ledwell “marks” parcels of water by releasing harmless dyes or chemicals from
ships and then measures the subsequent dispersion (sometimes for several years). Such work aids oceanographers
in understanding the circulation of the ocean and the transport of nutrients, plankton,
and pollutants in ocean ecosystems-- all of which are important to marine life
and to the ocean’s role in climate change.

Ledwell and colleagues, including Andrew Watson of the University of East Anglia
(England), developed the
techniques in the basins off Southern California in the 1980s, with advice and
encouragement from Wallace Broecker of Columbia University.
Over the past two decades, Ledwell has played a leading role in tracer release experiments
in the North Atlantic thermocline, in the deep Brazil
Basin, on the continental shelf off
New England, in the upper layers of the Sargasso Sea, and, most recently, in
the area of hydrothermal vents on the East Pacific Rise southwest of Mexico.

“Recognition of my work by my peers is the best affirmation of
the path I have taken,” said Ledwell. “Recognition of this sort is so rare, and
this award incites me to carry on.”

Ledwell grew up in Rockland, Mass., and attended Cardinal
Spellman High
School in nearby Brockton.
He was awarded a bachelor’s degree in physics from Boston
College, followed by a master’s in
physics from the University of Massachusetts at Amherst in 1974. He completed master’s and
doctoral degrees in applied physics from Harvard University
with Prof. Michael McElroy. He then became a postdoctoral research associate at
the Goddard Institute for Space Studies, with James Hansen, and a research
scientist at Columbia
University’s Lamont-Doherty
Earth Observatory, before joining WHOI in 1990. Ledwell is a member of the
American Geophysical Union, the American Meteorological Society, and The
Oceanography Society.

The Woods Hole Oceanographic Institution is a private,
independent organization in Falmouth,
Mass., dedicated to marine
research, engineering, and higher education. Established in 1930 on a
recommendation from the National Academy of Sciences, its primary mission is to
understand the oceans and their interaction with the Earth as a whole, and to
communicate a basic understanding of the ocean's role in the changing global
environment.

The National Academy of Sciences is a private, nonprofit
honorific society of distinguished scholars engaged in scientific and
engineering research, dedicated to the furtherance of science and technology
and to their use for the general welfare. Since 1863, the National Academy of
Sciences has served to "investigate, examine, experiment, and report upon
any subject of science or art" whenever called upon to do so by any
department of the government.

Originally published: February 7, 2007

WHOI is the world's leading non-profit oceanographic research organization. Our mission is to explore and understand the ocean and to educate scientists, students, decision-makers, and the public.